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Equinox, Solstice


ecliptequatorImage: hyperphysics.phy-astr.gsu.edu

 

The line of intersection between ecliptic and equator points at both ends to the so called spring and autumn equinox. This equinoctial direction is an important reference for astronomical co-ordinate systems.

Perpendicular to the line of the equinoxes is the line of the summer and winter solstice. These four points along the ecliptic are indicative for the four seasons on Earth. When the Sun crosses any of these points, there is a corresponding change of season, opposite for the two hemispheres.

The names of the solstices and equinoxes, refer to the seasons on the Northern hemisphere.

 

 

 

 

Animation: Freedman and Kaufmann

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Ecliptic in the sky

The Ecliptic is the Earth's orbital plane around the Sun. So from Earth we see the sun move along a line that we call the ecliptic. The Moon and the other planets have their orbits approximately in the same plane as well, and we see those move along the same ecliptic in the sky as well.

 

Because of the axial tilt, the ecliptic tilts and moves up and down in the sky throughout the year. The Sun passes the celestial equator at the vernal equinox at about 21 March (northern spring) and the autumnal equinox at about 22 September (northern autumn).

 

 

 

 

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